Performance Study: Daggerboards & Fixed Keels

[mark_morwood]

Originally Posted by CGirvan

If anyone has any links to info on controlling daggerboards I would really appreciate it.

http://www.cruisersforum.com/forums/...rds-14944.html

[Thumbs Up]

Wolfson unit...ok google...lots of simulations, makes me think that those polar charts are theoretical and not based on full scale actual performance trials (not that there is anything wrong with that). My point was that those polars would be more revealing if the data had been completed and plotted another 5 degrees into the wind. Phil Berman is actually a member but only has a few posts to his name (it could be dangerous for a broker here. CF can be pretty ruthless). As for centerboards (don't Geminis have them?), it seems like the kick-up feature is worth looking at. I don't think centerboards work well partially deployed, it has to be all or none.

[Training Wheels]

Originally Posted by mark_morwood

I suspect that like me, very few people here have experience with centerboards on catamarans so can't offer much in the way of informed comment so are keeping quiet. Yeah I know, when has that ever stopped anyone! :-)



I don't think I've ever knowingly seen a catamaran with centerboards, though I do know they exist. Sorry.

Ever seen a Gemini?

[mark_morwood]

Originally Posted by Training Wheels

Ever seen a Gemini?

Almost certainly from a distance, but haven't sailed on one, or even looked at one closely. Not really my style of boat, so haven't pursued them. I've got nothing against center boards, I was just suggesting a theory on why there weren't many comments about center boards on catamarans.

[Heath68]

Does anyone know why centreboards aren't very popular? I saw a video of the MC50 (gorgeous cat) just launched that has them, and if they're effective they take up a lot less space

[catsketcher]

I have only owned one multi with a centreboard and it was a big hassle compared to a daggerboard. There were a couple of reasons I didn't like it in the end.

1- it got barnacles in it. In a dagger case the case can be made to fit like a glove. The antifoul on the board keeps the case clean and some antifoul can go on the case too. But in a centreboard case there seem to be more places for a barnacle to grow unemcumbered by a board sliding by.

2- hydraulic stuff - when you go fast the noise gets pretty loud from roiling turbulence within the case. Racing multis have been know (in the 70s) to blow the to blow the tops of the case.

3 - access - you need ropes to pull the board up and down. These are more complicated than simple uphaul and downhauls.

4 - drag - the big slot in the bottom creates turbulence and drag.

5 - structure - you are putting a longer slit in the bottom of the boat which weakens it.

6 - hard to move - as you have little purchase on the board top with rope I found it harder to pull up or down.

7 - noise - the board had to be loose enough to rotate so it wobbled around in the slot

The MC 50 concept seems like a solution to a non problem. A well designed case takes up very little usable room and is well proven. I don't get this idea at all.

[thinwater]

Originally Posted by Training Wheels

Ever seen a Gemini?

Of course, for me. I sail near where they were first built and have sailed on them. The arc profile is a little non-standard, but no uncommon on day sailors. They go to weather better than most cruising cats and many are racer.



My PDQ had minikeels. I had upgraded them and the sails for better windward performance, but she was still boring to tack.

My F-24 has a center board with a dagger board profile. Tacks on a dime.

On one hand centerboards are more complex to build, slightly heavier by the time the box is included, and have some drag from the box opening. On the other hand hitting things is less hazardous and they are less prone to jamming.

[Jenta]

Not lending any experience or thoughts to the discussion, but adding in an overlay of the two polar charts in the article because it makes it easier to compare the charts for me. That is of course assuming the information in the charts is solid and useful information, which I am not qualified to ascertain.

[tp12]

Originally Posted by cuffy

The Wolfson unit, University of Southampton, have are probably one of the most respected yacht and ship research centres in the world.
Try google

Even the mighty can fall, it would seem. Designing a comparison using a scenario that incorrectly uses the boards downwind seems to me to be a waste of time. It certainly renders the downwind comparisons irrelevant.

[admiralslater]

I agree that not properly using the boards negates the test . For me the bigger failure was stopping at 45 degrees up wind

[rmd]

Originally Posted by thinwater

No comments on centerboards?

I have a centerboard on my TomCat 9.7. Seems to do well upwind and tacking but my only extended experience with another boat has been the very agile Farrier 25C trimaran, also with a centerboard. My one complaint is that the gear for raising and lowering the centerboard on the TomCat is too frail so I end up just leaving the board down most of the time.

[VBsail]

My Iroquois has a pair of canted centerboards. I have no complaints with them. They don't make noise or jam and are about neutral buoyancy. A single line raises and lowers them from the cockpit by hand. Similar to its kick up rudders. When in the up position they are shaped to close off the opening for efficiency. Downside is that shape is not as efficient when deployed. I generally leave them up most of the time and only lower them if I really want to point upwind a bit higher and its blowing above 12knots. They help during tight marina maneuvers and we generally use them each time we dock unless there is cross current. My cat is small, much more similar to a beachcat design than a modern cruiser.

[Russ333]

Dare I say, I think it's a very balanced article. The author is comparing an efficiently keeled cat, verse the same dagger-boarded (always down) cat. Results predictable and significant, not only for racing, but if you've ever tried to sail off a lee shore, or make an approaching headland hard on the wind. As stated, the comparison would be even starker if comparing a typical keeled charter cat verse a more performance driven dagger-boarded cat.
Two additional comments from experience, low profile fixed keels really suffer much greater performance degradation going to windward in short steep waves, as their hydro-dynamic performance gets totally disrupted. On the flip-side, more than once, I've been extremely glad of robust fixed keels and sked protecting the rudder, where only superficial damage was sustained. Not that I'm accident prone, but s... does happen when living aboard out in the wild.
Which do I prefer, well it depends ......

[44'cruisingcat]

Originally Posted by Russ333

.....
As stated, the comparison would be even starker if comparing a typical keeled charter cat verse a more performance driven dagger-boarded cat.

And the boards were used correctly....

[Dan GB]

Originally Posted by 44'cruisingcat

And the boards were used correctly....

Just as a reference, my Shuttleworth Spectrum has just one dagger board in the port hull. I read that John Shuttleworth was of the view that a second one added little benefit and decreased speed somewhat. This, I think was based on observations of first boat that had two. Mine is nr 3.

The dagger board in question is a beast of a thing, and has a rope pulley arrangement to a winch. When raised, I learned to not let its weight allow it to drop - the down haul rope bunched up and jammed beyond any hope of lifting. Had to use a forklift in the end...